Potentiometer



I Nov. I'7, 1967 v K. M. MERz 3,351,881

POTENTIOMETER Filed June 22', 1966 KENNETH M. MER! ATTORNEY United States Patent y 3,351,881 POTENTIOMETER Kenneth M. Merz, Malvern, Pa., assigner to IRC, Inc., Philadelphia, Pa. Filed June 22, 1966, Ser. No. 559,589 6 Claims. (Cl. 338-123) The present invention relates to a potentiometer, and more particularly, to a potentiometery having dual movable contacts which can be operated either independently or in unison.

A type of miniature potentiometer presently being used comprises a rectangular housing within which is mounted an elongated resistance element and a threaded shaft extending parallel to the resistance element. A contact is carried by the shaft and slidably engages the resistance element so that rotation of the shaft moves the contact along the resistance element. Terminals are provided for the contact and the ends of the resistance element. The range of resistance values of the potentiometer depends on the length of the resistance element and the resistivity of the resistance material of the resistance element.

One problem with this type of potentiometer, particularly in small units, is in providing a high range of resistance values yet be capable of accurately obtaining vany desired resistance value within the range. To obtain a high range of resistance values for a resistance element of a given length, it is necessary to use a resistance material having a high resistivity. However, when using a high resistivity resistance material the change in resistance provided by each increment of movement ofthe contact along the resistance element is relatively-large. Thus, it is diiicult to adjust the position of the contact along the resistance element to accurately obtain a desired resistance value. Therefore, it would be desirable to have such a 3,351,881 Patented Nov. 7, 1967 element providing fine changes in resistance value between g the increments of the one resistance element as its contact potentiometer which can provide a high range of resistance values yet permits accurately obtaining any desired resistance value within the range of values.

There are certain types of electrical circuits which include two potentiometers wherein it is sometimes desirable to be able to adjust the resistance values of both potentiometers uniformly yet, at other times, it is desirable to adjust the resistance values of the two potentiometers differently. Since it is diliicult to separately adjust two potentiometers uniform amounts, it would be desirable to be able to simultaneously adjust both potentiometers to obtain the uniform adjustment, but still be able to adjust at least one of the potentiometers independently of the other.

It is an object of the present invention to provide a novel potentiometer. l

It is another object of the present invention to provide a novel potentiometer having two separate movable contacts which pcan be operated either separately or in unison. It is still another object of the present invention to provide a potentiometer which can provide a high range of resistance values and yet permits accurately obtaining any desired resistance value within the range of resistance values.

It is a further object of the present invention to provide a potentiometer having two separate contacts slidably engaging separate resistance elements and carried on separate threaded shafts for movement along the resistance elements with the shafts being rotatable either in unison or separately. f

It is a still further object of the present invention to provide a potentiometer having two separate contacts slidably engaging separate resistance elements and carried on separate threaded shafts with one of the resistance elements providing incremental changes in resistance value as its contact slides therealong, and the other resistance moves therealong.

Other objects will appear hereinafter.

For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown. v

FIGURE 1 is a perspective view of the potentiometer of the present invention. v

FIGURE 2 is a sectional view taken along line 2-2 of FIGURE 1.

FIGURE 3 is a sectional view taken along line 3 3 of FIGURE 2.

FIGURE 4 is a sectional view taken along line 4-4 of FIGURE 2.

FIGURE 5 is a sectional view of FIGURE 2.

Referring to the drawing, the potentiometer of the present invention is generally designated as 10.

Potentiometer 10 comprises a rectangular housing 12 0f an electrical insulating material, such as a plastic. The length of the housing 12 is many times greater than its width and height. Housing 12 has a substantially rectangular cavity 14 in its bottom surface 16 providing the housing 12 with a top wall 18, a pair of side walls 20 and 22, a front end wall 24 and a back end wall 26. The front end wall 24 has a cylindrical bearing hole 28 therethrough extending between the outer and inner surfaces of the front end wall (see FIGURE 2). The bearing hole 28 is located intermediate the side walls 20 and 22 and adjacent the top wall 18. The back end wall 26 has a cylindrical bearing recess 30 in its inner surface. The axis of the bearing recess 30 is in alignment with the axis of the bearing hole 28. The front end wall 24 and back end wall 26 are provided with mounting holes 32 and 34 respectively extending therethrough between the side walls 20 and 22. The mounting holes 32 and 34 are positioned below the bearing hole 28 and the bearing recess 30 respectively. A bottom plate 36 of an electrical insulating material, such as a plastic, extends completely across the open end of the cavity 14 and is secured to the housing 12, such as by a suitable cement. The outer surface of the bottom plate 36 is flush with the bottomV surface 16 of the housing. Thus, the bottom plate 36 encloses the cavityl 14.

As shown in FIGURE 2, a drive shaft assembly, generally designated as 38, extends longitudinally across the taken along line 5-5 I cavity 1,4 adjacent the top wall 18 of the housing 12, and

is rotatably supported on the end walls 24 and 26. Drive shaft assembly 38 comprises two longitudinally aligned, threaded drive shafts 40 and 42. The front shaft 40 has a smooth, cylindrical head portion 44 on its front end n which extends through and is rotatably supported in the bearing hole 28. The head portion 44 projects beyond the outer surface of the front wall 24 and has a transverse slot 46 across its free end which is adapted to receive a screw driver or similar tool for rotating the front shaft 40. An annular groove 48 is provided in the surface of the head portion 44 within the bearing hole 28. A locking pin 50 extends through' the end wall 24 and across the annular groove 48 to limit longitudinal movement of the front shaft 40. The annular groove 4-8 is wider than the diameter of the locking pin 50 for reasons which will be explained later. An elongated bearing pin 52 is iixedly secured to and extends longitudinally from the back end of the front shaft 40 along the longitudinal axis of the front shaft. The back end surface of the front shaft 40 is provided with a plurality of radially extending serrations 54.

The back shaft 42 has a cylindrical bearing pin 56 on its back end which extends into and is rotatably supported in the bearing recess 30 in the back end wall 26. The front end of the back shaft 42 has a blind hole 58 therein extending longitudinally along the axis of the back shaft. The blind -hole 58 is larger than the length of the bearing pin 52 which rotatably fits therein. A helical spring 60 is seated in the blind hole 58 and is compressed between the bottom of the blind hole 58 and the end of the bearing pin 52. The spring 60 normally holds the adjacent ends of the front shaft 40 and the back shaft 42 apart. The front end surface of the back shaft 42 is provided with a plurality of radially extending ser-rations 62 which can mate with the serrations 54 on the end of the front shaft 40. In the normal position of the shafts 40v and 42 with their adjacent ends held in spaced apart arrangement by the spring 60, the front shaft 40 can be rotated independently of the back shaft 42. However, by pressing longitudinally inwardly on the front shaft 40, the serrations 54 on the front shaft are brought into rotating engagement with the serrations 62 on the back shaft 42 so that rotation of the front shaft also rotates the back shaft.

Separate contact carriers 64 and 66 are mounted on the front shaft 40 and back shaft 42 respectively. Each of the contact carriers 64 and 66 comprises a rect-angular block of an electrical insulation material, such yas a plastic, having a hole therethrough, though which the shafts 40 and 42 are threaded. As shown in FIGURE 3, each of the contact carriers 64 and 66 is of a width substantially equal to the distance between the side walls 20 and 22 of the housing 12. Thus, upon rotation of the shafts 40 and 42, the contact carriers 64 and 66 are moved longitudinally along the shafts. A stop lug 68 extends -downwardly from the inner surface of the top wall 18 of the housing 12 at the adjacent ends of the shafts 40 and 42. Thus, the longitudinal movement of the contact carrier 64 along the front shaft 40 is limited by engagement with the front end wall 24 of the housing 12 or the stop lug 68, and the longitudinal movement of the contact carrier 66 along the back shaft 42 is limited by engagement with the back end wall 26 of the housing 12 or the stop lug 68.

A pair of longitudinally aligned resistance elements, generally designated as 70` and 72 respectively, are mounted on the bottom plate 36 parallel to the shafts 40 and 42. As shown, the resistance elements 70 and 72 are formed on a single, elongated, cylindrical substrate 74 of an electrical insulation material, such as a ceramic. However, if desired, the resistance elements 70 and 72 can be formed on separate substrates. The resistance element 70 comprises a continuous film 76 of a resistance material coated on the surface of the front portion of the substrate 74. The resistance material can be any of the well-known resistance materials, such as a metal, lmetal alloy, mixture of metals, carbon or conductive particles embedded in an insulating material such as glass or plastic. Termination bands 78a and 7812 of an electrically conductive metal, such as silver or copper, are applied around the substrate 74 at the ends of the resistance film 76 and contact the resistance film 76. As shown in FIGURE 2, terminal wires 80a and 80h extend through the bottom plate 36 and are electrically connected to the termination bands 78a and 78b respectively. Resistance element 72 comprises a suitable resistance material 82 extending around and along the back portion of the substrate 74 in a helical path. Resistance material 82 may be either a film coated on the substrate or a Wire wound therearound. Termination bands 84a. and 84b of an electrically conductive met-al are provided around the substrate 74 and the ends of the resistance material 82, and are electrically connected thereto. Terminal wires 86a and 86b extend through the bottom plate 36 and are electrically connected to the termination bands 84a and 84h respectively. As shown in FIGURE 3, the resistance elements 70 and 72 are seated in a groove 88 in the bottom plate 36 and are secured therein by a suitable electrically non-conductive cement.

A pair of collector strips 90 and 92 of an electrically conductive metal are mounted in longitudinal alignment on the bottom plate 36 adjacent and parallel to the resistance elements 70 and 72 respectively (see FIGURE 4). The collector strips 90y and 92 are each of the same length as their respective resistance elements 7 0 and 72. As shown in FIGURE 3, each of the collector strips 90 and 92 is secured in a groove in the bottom plate 36 land the top edge of the collector strip is bent over to provide a rounded, contact surface. Terminal wires 94 and 96 extend through the bottom plate 36 and are electrically connected to the collector strips 90 and 92 respectively.

Contact Amembers 98 and 100 of an electrically conductive metal are secured to the bottom surfaces of the contact carriers 64 and 66 respectively. Contact member 98 has a pair of spaced, parallel contact arms 102 and 104 extending downwardly therefrom which terminate in rounded contact lips 102a and 104a respectively. The contact lip 102a slidably engages the resistance film 76 of resistance element 70, and the contact lip 104a slidably engages the collector strip 90. Thus, the resistance element 70 is electrically connected to the collector strip 90 through the contact member 98. Contact member also has a pair of spaced, parallel contact arms 106 and 108 extending downwardly therefrom which terminate in rounded contact lips 106-a and 108a respectively. The contact lip 106a slidably engages the resistance material 82 of the resistance element 72, and the contact lip 108a slidably engages the collector strip 92. Thus, the resistance element 72 is electrically connected to the collector strip 92 through the contact member 100.

The potentiometer 10 of the present invention can be used to provide a high range of resistance values yet is capable of accurately obtaining any desired resistance value within the range. The helical resistance path 82 of the back resistance element 72 provides a long, narrow resistance path so that the total resistance value between the termination bands 84a and 84b is relatively high. However, as the contact arm 106 moves along the resistance element 72, the resistance Value between one of 4the termination bands, for example the termination band 84a, and the contact arm 106 varies incre-rnently depending on the resistance value of each turn of the resistance material 82. The short, continuous resistance film 76 of the resistance element 70 has a total resistance value between the termination bands 78a and 78b which is relatively small. For this use of the potentiometer 10, the total resistance value of the resistance element 70 is designed to be substantially equal to the resistance value of one turn of the helical resistance path 82 of the resistance element 72. Since the resistance film 76 of the resistance element 70 is continuous along the entire path of travel of the contact arm 102, the resistance value between one of the termina tion bands, for example the termination band 78a, and the contact arm 102 varies continuously as the Contact arm 102 moves along the resistance film 76. Thus, the resistance element 70 provides an infinite number of resistance values Within its total resistance value.

For one way of using the potentiometer 10 for this purpose, the collector strip terminal wires 94 and 96 are electrically connected together, and the resistance is measured between one of the terminal wires of the resistance element 70, for example the terminal wire 80a, and one of the terminal Wires of the resistance element 72, for example the terminal wire 86a. Thus, the resistance being measured is the resistance value of the resistance element 72 between the termination band 84a and the contact arm 106 plus the resistance value of the resistance element 70 between the termination band 78a and the contact arm 102. Instead of connecting the collector terminal wires 94 and 96, the collector strips 90 and 92can be electrically connected inside the housing 12 or can be made of a single strip of metal. To obtain a desired resistance value, the front shaft 40 is pressed inwardly and rotated so as to rotate the rear shaft 42 as previously described. Rotation of the rear shaft 42 moves the contact arm 106 along the resistance element 72. The contact arm 106 is so moved along the resistance element 70 until the resistance value between the terminal wire 86a and the contact arm 106 is slightly less than the desired resistance value. This provides a coarse adjustment of the resistance value of the potentiometer 10. The front shaft 40 is then released to its normal position shown in FIGURE 2 and rotated to move the contact arm 102 along the resistance element 76 until the desired resistance value is obtained. This provides the ne adjustment of the resistance value of the potentiometer 10. Since the resistance element 72 provides incremental changes in resistance value over a wide range of values, and the resistance element 76 provides an infinite number of resistance values over a range equal to the incremental change of the resistance element 72, the potentiometer of the present invention can accurately provide any desired resistance value over a wide range of values.

Another way of using the potentiometer 10 for this purpose is to electrically connect the resistance elements 70 and 72 in series. This can be achieved internally of the housing 12 by electrically connecting the termination bands 78b and 84a or externally of the housing by electrically connecting the terminal wires 80b and 86a. An input voltage is applied across the resistance elements 70 and 72 through the terminal Wires 80a and 86h. The output is measured across the terminal wires 94 and 96 of the contacts 9-8 and 100. By pressing inwardly on the front shaft 40 and rotating the shafts 40 and 42, the contact arm 106 is moved along the resistance element 72 until a coarse adjustment of the potentiometer is obtained. The front shaft 40 is then released and rotated to move the contact 102 -along the resistance element 70 until the fine adjustment is obtain-ed. Thus, the resistance value being measured is the resistance value of the resistance element 70 'between the contact arm 102 and the termination band 78b plus the resistance value of the resistance element 72 between the termination band 84a and the contact arm 106. Other Ways of using the potentiometer 10 for this purpose are obvious to one skilled in the art. Although the resistance material 82 of the resistance element 72 is shown in the form of a helical path to achieve a resistance element having a high resistance, such a high resistance can also be obtained using a continuous tilm of a high resistivity resistance material.

The potentiometer 10 can also be used to provide two separate variable resistors which can be adjusted either simultaneously or separately. By pressing in on the front shaft 40 and rotating the front shaft 40, the back shaft 42 is also rotated so that both contact arms 102 and 106 are simultaneously moved along their respective resistance elements 70 and 72. Thus, the resistance values provided by the resistance elements 70 and 72 are adjusted simultaneously. When the front shaft 40 is released to its normal position shown in FIGURE 2, rotation of the front shaft 40 only moves the contact 102 along the resistance element 70 so that the resistance value of only the resistance element 70 is adjusted. For this use of the potentiometer 10, the resistance elements 70 and 72 may be different or identical depending on the requirements of the electrical circuit in which the potentiometer is to be used. Thus, the resistance material of both of the resistance elements may be in the form of a continuous film, such as that shown for the resistance element 70, or in the form of a helical path, such as shown for the resistance element 72, or either one may be in the form of `a continuous film and the other as a helical path. Also, the resistance values of both of the resistance elements may 'be identical or different.

The present invention may be embodied in other speciiic forms without departing from the spirit or essential attributes thereof, and, accordingly, reference should be made to the appended claims, rather than to the foregoing specication as indicating the scope of the invention.

I claim:

1. A potentiometer comprising a substantially rectangular housing having an enclosed cavity therein, a pair of longitudinally aligned, threaded shafts extending across the cavity and rotatably supported on said housing, one end of one of said shafts extending through a wall of said cavity and being accessible from outside said housing for actuating the shafts, means normally holding the adjacent ends of said shafts in spaced apart relation but permitting longitudinal movement of said one shaft to bring said adjacent ends into engagement, means on the adjacent ends of said shafts providing a driving connection between said shafts when the adjacent ends are in engagement so that rotation of said one shaft also rotates the other shaft, a pair of longitudinally aligned electrical resistance elements mounted on said housing Within said cavity and parallel to said shafts, a separate electrically conductive contact member carried by each of said shafts for longitudinal movement along said shafts 4upon rotation of the shafts, each of said contacts slidably engaging a separate one of said resistance elements, and terminals extending through said housing and electrically connected to said resistance elements.

2. A potentiometer in accordance with claim 1 including electrically conductive collector strips mounted on the housing within the cavity and parallel to the resistance elements, and each of said contacts also slidably engaging a collector strip.

3. A potentiometer in accordance with claim 2 in which each of the resistance elements comprise a substrate of an electrically insulating material and a resistance material on the surface of the substrate, and each of the contacts slidably engages the resistance material of its respective resistance element.

4. A potentiometer in accordance with claim 3 in which the resistance material of one of the resistance elements extends in a helical path around and along the substrate, and the resistance material of the other resistance element is a film coated on its substrate and providing a longitudinally continuous resistance path.

5. A potentiometer in accordance with claim 4 in which the maximum resistance value of the resistance material of the other resistance element is substantially equal to the resistance value of one turn of the helical resistance path of the one resistance element.

6. A potentiometer in accordance with claim 5 in Which the resistance element having the longitudinally continuous resistance path is engaged by the contact carried by the one said shaft and the resistance element having the helical resistance path is engaged by the contact carried by the other shaft.

ROBERT K. SCHAEFER, Primary Examiner. H. J. HOHAUSER, Assistant Examiner. 

1. A POTENTIOMETER COMPRISING A SUBSTANTIALLY RECTANGULAR HOUSING HAVING AN ENCLOSED CAVITY THEREIN, A PAIR OF LONGITUDINALLY ALIGNED, THREADED SHAFTS EXTENDING ACROSS THE CAVITY AND ROTATABLY SUPPORTED ON SAID HOUSING, ONE END OF ONE OF SAID SHAFTS EXTENDING THROUGH A WALL OF SAID CAVITY AND BEING ACCESSIBLE FROM OUTSIDE SAID HOUSING FOR ACTUATING THE SHAFTS, MEANS NORMALLY HOLDING THE ADJACENT ENDS OF SAID SHAFTS IN SPACED APART RELATION BUT PERMITTING LONGITUDINAL MOVEMENT OF SAID ONE SHAFT TO BRING SAID ADJACENT ENDS INTO ENGAGEMENT, MEANS ON THE ADJACENT ENDS OF SAID SHAFTS PROVIDING A DRIVING CONNECTION BETWEEN SAID SHAFTS WHEN THE ADJACENT ENDS ARE IN ENGAGEMENT SO THAT ROTATION OF SAID ONE SHAFT ALSO ROTATES THE OTHER SHAFT, A PAIR OF LONGITUDINALLY ALIGNED ELECTRICAL RESISTANCE ELEMENTS MOUNTED ON SAID HOUSING WITHIN SAID CAVITY AND PARALLEL TO SAID SHAFTS, A SEPARATE ELECTRICALLY CONDUCTIVE CONTACT MEMBER CARRIED BY EACH OF SAID SHAFTS FOR LONGITUDINAL MOVEMENT ALONG SAID SHAFTS UPON ROTATION OF THE SHAFTS, EACH OF SAID CONTACTS SLIDABLY ENGAGING A SEPARATE ONE OF SAID RESISTANCE ELEMENTS, AND TERMINALS EXTENDING THROUGH SAID HOUSING AND ELECTRICALLY CONNECTED TO SAID RESISTANCE ELEMENTS. 